The present invention relates to a method and a device for steadying an aircraft with a view to a maintenance operation.
When an aircraft must undergo a maintenance operation directed in particular at its structure, for the purposes of verification and/or servicing and/or repair, it is often necessary to steady it by means of jack props in order to eliminate or at least limit the stresses occurring in the aircraft zone, referred to as working zone, affected by the maintenance operation.
It is important that the stress level caused in the working zone be as low as possible. In fact, during removal of a fastener in the working zone, a stress level that is too high makes it necessary to force the fastener, and in such a case the risk is high that the hole receiving the fastener will be warped. When such an incident occurs, it is then necessary to enlarge the hole diameter and to change the fastener diameter. But this cannot be repeated indefinitely, and the capacity of the aircraft to be repaired diminishes with each maintenance operation. In addition, inappropriate steadying also causes risks of deformation of the aircraft structure (in the working zone) in the case of removal of a large number of fasteners.
It should be noted that steadying must also be achieved while keeping the level of stresses occurring outside the working zone under control.
To permit such steadying, the aircraft structure usually comprises a plurality of anchoring points on which the props are anchored. The total number of props that can be used and their respective positioning are therefore defined in phases of design and manufacture of the aircraft. Within the scope of a maintenance operation, depending on the zone in question, it nonetheless is not necessary to position all of the props. In addition, the load that each prop must apply to the aircraft varies according to the working zone, the type of operation and the configuration of the aircraft. This is why the technicians generally establish, during the design of the aircraft, a list of usual operations, referred to as reference operations, which not uncommonly have to be performed during the life of the aircraft, as well as the corresponding working zones; they then establish a map of props to be used (or in other words, support points to be provided) and of loads to be applied per prop for each of these reference operations and/or for each of these working zones.
Within the scope of a maintenance operation corresponding to a reference operation, the application of the corresponding map of support points guarantees that the stresses that may be sustained by the aircraft structure in the working zone are normally lower than a given level at which the integrity of the aircraft structure can be preserved. However, the actually obtained stress level is rarely zero and often not low enough to permit removal of the fasteners without forcing them and to avoid the corresponding risks.
Furthermore, when an uncommon and unforeseen maintenance operation, or in other words one not corresponding to a reference operation (which is often the case during structural repairs), must be undertaken, the aforementioned maps cannot be used. It is then necessary to defined, by calculation, the props to be used and the corresponding loads to be applied. These calculations are performed on a simplified model of the aircraft wherein, for example, the fuselage and the wings of the aircraft are modeled by three beams (one beam for each aforesaid element). Consequently they yield very imprecise results, which do not make it possible to guarantee the desired stress level in the working zone. Furthermore, despite the allowed simplifications, these calculations are lengthy and must be performed by the aircraft manufacturer, thus creating additional delays that may last as long as one day. The costs of executing the calculations are increased by those resulting from downtime of the aircraft.
In addition, it may occur, during a maintenance operation, that previously undetected damage is discovered or else that a modification of the aircraft configuration is to be made (removal of an element that changes the weight of the aircraft, etc.). This then makes it necessary to recalculate the props, prolonging the duration of downtime of the aircraft even more. In addition, given that the calculations are based on a ratio that may contain errors and not on the real configuration of the aircraft, it cannot be ruled out that the initially planned props will have the effect of increasing the stresses in the damaged zone to the point that they may jeopardize the aircraft structure.